Defloccing roll for paper machine headboxes



Empt -m;-

Nov. 1, 1955 Filed Aug. 15, 1950 R. D. DUNCAN 2,722,164

DEFLOCCING ROLL FOR PAPER MACHINE HEADBOXES 2 Sheets-Sheet l INVENTOR@985 T D. Du/vcm/v.

AGENT.

1955 R. D. DUNCAN DEFLOCCING ROLL FOR PAPER MACHINE HEADBOXES 2Sheets-Sheet 2 Filed Aug. 15, 1950 United States Patent DEFLOCCING ROLLFOR PAPER MACHINE HEADBOXES Robert D. Duncan, Gatineau, Quebec, Canada,assignor to Canadian International Paper Company, Montreal, Canada, acorporation of Quebec Application August 15, 1950, Serial No. 179,586

3 Claims. (Cl. 9244) This invention relates to new and usefulimprovements in paper machine headboxes and particularly seeks toprovide novel apparatus especially useful to break up any flocformations which may occur in a flowing pulp suspension.

This invention comprises a defioccing roll usable with any type ofheadbox having a substantial channel portion ahead of the slice, but isparticularly designed to break up such floc formations as may develop ina stock suspension moving under frozen flow conditions. An example of aheadbox capable of establishing frozen flow conditions in the stocksuspension may be found in copending application Ser. No. 157,869, filedApril 25, 1950, by Weston T. Bennett, and the defioccing roll of thepresent invention has been expressly designed to operate in conjunctionwith a headbox of the type disclosed therein.

An object of this invention, therefore, is to provide a cage type ofdefioccing roll for paper machine headboxes.

Another object of this invention is to provide a device of the characterstated positioned within a channel portion of a headbox and rotatableabout a transverse axis with respect to the direction of flow of stocksuspension.

Another object of this invention is to provide a device of the characterstated which comprises a pair of header discs, a plurality of spacingdiscs between the header discs, a plurality of circumferentially spacedrods adjacent the periphery of the discs to form a cylindrical cage typedefioccing roll and stub shafts extending outwardly from each headerdisc for rotatably mounting the defioccing roll.

A further object of this invention is to provide a device of thecharacter stated in which the diameter of the cylinder cage is at leasttwice the depth of the flowing stock suspension in which the defioccingroll is partially immersed.

A further object of this invention is to provide a de vice of thecharacter stated in which the spacing of the cage-forming rods is suchthat the sum of the diameters of all of the rods is equivalent to from16% to 27% of the circumference of the circle passing through the centerlines of the rods.

A further object of this invention is to provide means for rotating thedefioccing roll preferably in the direction of the flow of the stocksuspension.

With these and other objects in view, the nature of which will be moreapparent, the invention will be more fully understood by reference tothe drawings, the accompanying detailed description, and the appendedclaims.

In the drawings,

Fig. l is a somewhat diagrammatic side elevation of a paper machineheadbox and shows a defioccing roll constructed in accordance with thisinvention installed there- Fig. 2 is a transverse section taken alongline 22 of Fig. 1;

Fig. 3 is a perspective view of the defioccing roll;

Fig. 4 is an end elevation thereof;

Fig. 5 is an enlarged detail longitudinal section adjacent the peripheryof one end of an installed defloccing roll; and

Fig. 6 is an enlarged detail longitudinal section at the same end of thedefioccing roll but showing the central portion thereof.

It is characteristic of papermaking fibers in water suspension to flocinto more or less independent aggregates. The degree of suchflocculation is dependent in particular upon the physical nature of thefibers, their concentration (stock consistency) and the fluid flowconditions of the suspension. When the type and concentration of stockbeing handled range over relatively narrow limits as in the case ofnewsprint headbox stock it is the fluid flow conditions which areparamount in either inducing or minimizing floc formation. Thus if abody of flowing newsprint headbox stock is made sufiiciently turbulentby agitation, pumping, high velocity flow, etc., a'

random pattern of velocity gradients between parallel planes of thesuspension are created which are of such magnitude and number that thedegree of flocculation of the fibers is only slight (small floc size) ordoes not occur at all. Under such conditions flocculation and flocgrowth are prevented or minimized because the characteristic flocstructure has not suflicient strength to withstand the overwhelmingforces on the fibers resulting from the shear zones established betweenthe velocity gradients. If the turbulence in this body of stock iscaused to gradually diminish, velocity gradients are approached whichpromote flocculation by bringing about contact between fibers and fiberflocs resulting in a condition where the strength of the floc structureis more nearly in balance with the forces tending to pull it apart andhence both floc growth and deterioration may occur concurrently. Withfurther reduction in turbulence conditions of flow'will be approached atwhich the rate of growth and size of the floc is at or near a maximum.Finally, if the body of stock of greatly reduced turbulence is picturedas flowing in a wide channel at a velocity below the critical forturbulent flow and all turbulence has been eliminated from it the typeof flow thereupon established is termed frozen flow which ischaracterized by a thin shear zone adjacent to any surface of thechannel contacted by the stock in which the fibers tend to roll or shearpast one another while all the rest of the cross-section of the flowingstock suspension appears to be frozen into a solid moving parallel tothe axis of the channel and with uniform velocity throughout itscross-section. Once the frozen flow condition has been established thereis no movement of the fiocs in relation one to the other, and thus thefloc pattern is fixed.

In a headbox so designed that stock is conducted to the slice in afrozen flow state the smaller the floc size in the stock approaching theslice the smaller will be the floc size in the finished paper sheet. Inthe interest of obtaining a sheet of uniform fiber distribution,commonly described as close-up or well-filled, it is desirable tominimize the floc size going to the slice. A defioccing roll constructedin accordance with this invention meets this need, and its design andoperation are particularly applicable to a headbox capable ofestablishing frozen flow conditions in the stock ahead of the slice.

It has been observed when a small obstacle is held in a channel in whichflocced newsprint headbox stock is flowing in a frozen flow conditionthat in the downstream direction from the obstacle will be a long pathof well-deflocced stock. The degree of the defioccing and the period forwhich it persists is dependent on the nature of the turbulence which theobstacle induces. This indicates that if flocced stock in a frozen stateof flow can be mechanically deflocced in a suitable manner the defloccedsta e will persist by virtue of its frozen or near frozen flow conditionlong enough to pass through a slice. The defioccing roll constructed inaccordance with the present invention provides the mechanical means bywhich such defioccing actionmay be effected.

The action of the defioccing roll constructed in accord ance with thisinvention is to introduce many shear zones (turbulence) of uniformpattern and strength across the full width and depth .of the frozen flowbody of stock moving in the channel. The uniformity of the pattern ofthis turbulenceand its strength are such that the body of stock againassumes a frozen flow condition a short distance downstream from thedefioccing roll and the fioc size is uniform and has been greatlyreduced or eliminated.

Referring to the drawings in detail, it will be seen that the inventionas illustratedis embodied ina paper machine head box comprising anintake portion A, a relatively long horizontal channel portion B and anadjustable slice C. A defioccing roll D constructed in accordance withthis invention is installed in a horizontal channel B in either of thetwo positions indicated in Fig. l in the drawings.

The horizontal channel portion B is a closed conduit and includes abottom 5, side walls 6, 6 and a top (not shown) and receives aconstantflow of an aqueous pulp suspension from the intake portion Aunder such conditions that frozen flow becomes established as the pulpsuspension flows along the channel portion B.

One side wall 6 is provided with a circular aperture 7 closed by a covercasting 8 and secured to the side wall as by a plurality of bolts 9. Thecenter of the cover casting 8 is provided with a hub 10 bored to receivea bushing 11 and an adjustable packing gland 12 for rotatably receivinga stub shaft of the defioccing roll, as will be hereinafter more fullydescribed.

The other side wall 6 is similarly provided with an aperture closed by acover casting 13 secured to the side wall as by'a plurality of bolts 14.The center of the cover casting 13 is provided with a. hub 15 recessedto carry a bushing 16 for rotatably receiving a stub shaft extendingfrom the adjacent .end of the defioccing roll, as will be hereinafterrnore fully described.

The defioccing roll D per se includes a pair of header or end discs .17,17 provided on their outer faces with number of relatively smalldiameter rods or tubes 20 disposed in parallelism to form together withthe header discs 17 a cage-like roll. The central portions of the rods20 are held in their cylindriform relationship as by a plurality ofrelatively thin spacer discs 21 having the same diameter as the enddiscs 17 and similarly drilled adjacent their peripheries. The diametersof the rods 20 will be subject to such variations as may be required dueto the use of different types of stock as will the spacing betweenadjacent rods. However, for illustrative purposes if it were assumedthat a defioccing roll constructed in accordance with this invention isto be used in connection with newsprint headbox stock smooth rodsof inchdiameter represent the optimum. Smaller diameter rods tend to gatherfibers and would be a potential cause of stock lump formations, Whilelarger diameter rods produce a less uniform defioccing action and have anarrower range of operating speeds within which to produce the desiredtype of defioccing results. Similarly, for .newsprint stocks, thespacing between adjacent rods has been found to be at an optimum whenthe sum of the rod diameters comprising the roll face is equivalent to20% of thecircumference of the circle normal to the longitudinal axis ofthe roll and passing through the center lines of the rods. While theabove mentioned figure of 20% represents the optimum, reasonablysatisfactory results can be achieved with defioccing rolls in which thsum of the rod diameters is equivalent to from 16% to 27% of thecircumference of the pitch circle passing through the center lines ofthe rods.

The necessity for so regulating the rod spacing in order to achievesatisfactory defioccing action automatically provides means fordetermining the exact number of rods to be used in constructing adefioccing roll of any given diameter of pitch circle passing throughthe center lines of the rods. Thus for a roll of 24 inch pitch circlediameter using A inch diameter rods, sixty rods would have to be used inorder to meet the 20% optimum rod spacing determination. Alternately,for other types of stock or for different operating speeds it might befound desirable to employ rods of, say, /2 inch diameter in a defioccingroll having a pitch circle of 24 inches, in which case only thirty rodswould be required to meet the 20% spacing optimum. Similarly, if rods ofinch diameter were used on a 24 inch roll, one hundred twenty of themwould be required to meet the same spacing optimum. It will beappreciated, of course, that defioccing rolls of different pitch circlediameters will require corresponding variations in the number of rodsused in the construction of each roll.

One end disc 17 carries a relatively long stub shaft 22 which isjournalled in the bushing 11 of the cover casting 8 and extends beyondthe packing gland 12 a distance sufiicicnt tosupport a driving gear 23rigidly affixed thereto. The other end disc .17 carries a relativelyshort stub shaft 24 journalled in the bushing 16 of the cover casting13.

The defioccing roll D is adapted to be driven in a counterclockwisedirection as viewed in Fig. l of the drawings through the medium of areduction gear driving unit generally indicated at 25 and drive chain 26extending between it and the gear 23.

The, most favorable speed range is from 5 to 15 R. P. M. with 8 to 10 R.P. M. representing the optimum for a roll having a diameter of about 24inches when immersed in a stream of frozen flow headbox stock of about 8inches depth. It will be appreciated that the above rotative speeds androll diameter are also subject to considerable variations due to varyingdepths of the stream of stock and to types of stock being used.

The axis of rotation of the defioccing roll should always be positionedat such a height that the lower edge f the installed roll shall come asclose as possible to the bottom 5 of the headbox horizontal channelportion, and the clearance therebetween preferably should not exceed /2inch. It will be appreciated that the length of the defioccing roll issubstantially equal to the width of the associatedheadbox channelportion which is in turn substantially equal to the width of the papermachine wire. In those cases where defioccing rolls are to be employedwith wideheadboxes there may be some tendency for the central portion ofthe defioccing roll to sag downwardly toward contact with the bottom ofthe headbox. In such cases it has been found to be entirely practical toemploy a pair of very short trunnions (not shown) under each of thespacing-discs 21 whereby to support the central portion ofthis cage-typedefioccing roll.

I claim:

1. In combination with a paper machine headbox wherein is provided anintake portion, a relatively long horizontal portion for establishingfrozen flow conditions in the stock and a slice at the discharge endthereof; a defioccing roll rotatably mounted within the horizontalportion of said headbox and including a pair of end discs havingplurality of rods extending therebetween and arranged in cylindriforrnrelationship concentric with the axis of rotation of said roll, means tosupport the central portions of said rods against flexing, and means forrotating said roll, the spacingbetween center lines of said rods beingestablished by having the sum of the diametersof said rods equivalent tofrom 16% to 27% of the circumference of the circle passing through thecenter lines of said rods in a plane normal to the longitudinal axis ofsaid defloccing roll.

2. Defloccing mechanism for paper machine headboxes comprising a headboxchannel portion including bottom and side walls for conducting a flowingstream of headbox stock, a cage-type defloccing roll rotatably carriedby the side walls of said channel portion and including a plurality ofclosely spaced rods arranged in cylindriform relationship, the said rollbeing so positioned within said channel that at least the lower portionthereof is immersed in the flowing stream of stock, means to support thecentral portions of said rods against flexing, and means for rotatingsaid roll, the spacing between center lines of said rods beingestablished by having the sum of the diameters of said rods equivalentto from 16% to 27% of the circumference of the circle passing throughthe center lines of said rods in a plane normal to the longitudinal axisof said defloccing roll.

3. A defloccing roll for paper machine headboxes comprising a pair ofend discs, a plurality of rods extending between said end discs andarranged in cylindriform relationship, a plurality of spacer discslocated intermediate said end discs for supporting the central portionsof said rods against flexing, and an outwardly extending stub shaftcarried by each said end disc, the spacing between center lines of saidrods being established by having the sum of the diameters of said rodsequivalent to from 16% to 27% of the circumference of the circle passingthrough the center lines of said rods in a plane normal to thelongitudinal axis of said defloccing roll.

References Cited in the file of this patent. UNITED STATES PATENTS329,601 Smith Nov. 3, 1885 986,415 White Mar. 7, 1911 1,629,088 AldrichMay 17, 1927 1,667,755 Valentine May 1, 1928 1,753,201 Edlich Apr. 8,1930 2,152,264 Loft Mar. 28, 1939 2,390,977 Williams Dec. 11, 19452,566,449 Hornbostel Sept. 4, 1951

